1. Field of the Invention
The invention relates in general to an accessing apparatus and an accessing method thereof, and more particularly to an accessing apparatus and an accessing method thereof capable of reducing power consumption.
2. Description of the Related Art
Current digital apparatuses such as digital camera, MP3 walkman, personal digital assistant (PDA) and mobile phone all require a large capacity for the storage and accessing of data. Typically, data are accessed via an external memory card. The user can purchase various memory cards according to the required storage and accessing capacity. However, memory card possessing the advantage of convenience in exchanging data can transmit data with a computer via a card reader.
Referring to FIG. 1, a block diagram of a conventional accessing apparatus and a host is shown. Examples of the accessing apparatus 120 include a memory card with CF, SD or MS specification. Examples of the host 110 include an apparatus such as card reader or digital camera capable of accessing a memory card. The accessing apparatus 120, when electrically connected to the host 110, transmits a data D1 with the host 110 by using an external clock C1. The accessing apparatus 120 includes a buffer 121, a memory unit 123 and an oscillator 125.
The accessing apparatus 120 transmits the external data D1 with the host 110 by using the external clock C1, and enables the memory unit 123 and the buffer 121 to access an internal data D2 by using an internal clock C2. The internal clock C2 is generated by the oscillator 125. The buffer 121 is used for temporarily storing the external data D1 and the internal data D2. The external data D1 corresponds to the internal data D2. The memory unit 223 is used for storing the internal data D2.
When the host 110 is reading/writing the accessing apparatus 120, by incorporating the transmission width of data bus of the external data D1 with the external clock C1, the external data D1 is transmitted at a corresponding external band width BW1. Likewise, the internal data D2 is transmitted by using a corresponding internal band width BW2 of the internal clock C2 of the accessing apparatus 120. The accessing apparatus 120 may go with different hosts, that is, may go with different external clocks. Typically, in the case when the frequency of the external clock provided by the host 110 is unknown to the accessing apparatus 120, the internal clock C2 of the accessing apparatus 120 is enabled to operate at the highest frequency, avoiding the occurrence of buffer overrun or buffer underrun during the transmission of data. Thus, if the host 110 uses the slower external clock C1 but the accessing apparatus 120 still uses the faster internal clock C2, the internal clock C2 will be waiting for the external clock C1 for most of the time. When the internal clock C2 is waiting for the external clock C1, the state of high frequency is maintained, thus resulting in unnecessary power consumption. Take the portable electronic apparatus for example. Since the apparatus has only limited power supply, if unnecessary power consumption can not be avoided, the lifespan of the battery will be affected, deteriorating the competitiveness of the product.